1. Field
This application generally relates to rotational adjustments and particularly to a depth adjustment mechanism for a power tool, such as a router, planer, and the like.
2. Prior Art
This application relates generally to an adjustment mechanism for power tools and, more particularly, to an improved lift mechanism for adjusting the depth of a router mounted under a router table in an inverted position. This improved lift mechanism makes it easier to adjust the position of plunge and standard fixed base routers relative to the work supporting surface commonly known as a router table.
It is well known routers are popular power tools used by woodworkers. There are two main varieties of routers, standard routers, often called fixed base routers and plunge routers. The embodiment functions equally and similarly on both types of routers. The functionality will be described on a plunge router. A plunge router primarily consists of a motor mounted in a housing which drives a central shaft that engages a cutting bit. Many different types of cutting bits may be mounted to the central shaft and used for cutting different profiles in wood. A typical plunge router has a base mounted to it and is spaced apart from the router housing by one or more plunge rods fitted within recesses of the router housing. The distance between the housing and base are adjustable as the plunge rods act in a telescoping manner permitting the router housing and its cutting bit to slide along the plunge rods toward the base so that the cutting bit is brought into contact with the wood the base sits on. The base has a hole through which the cutting bit protrudes below the base into the wood being cut. The depth of the cut is set by adjusting the distance between the base and the router housing. Once the depth is set the woodworker drags the router across or into the wood to be cut.
To set the desired depth of the cut, a typical plunge router is equipped with a long, threaded adjustment rod which projects from the router base and through a portion of the router housing. To adjust the cutting depth, a woodworker rotates a nut along the threaded stop rod to set the depth of the cut the cutting bit makes. This adjustment is typically done with a wrench or a knob which engages the nut. These adjustments are easily done when the plunge router is used as a handheld tool.
Plunge routers have become popular with woodworkers that invert their plunge router, mounting them to the underside of a router table. This eliminates the need for the woodworker to handhold the router. The woodworker then feeds the material to be routed along the router table into the cutting bit. When so mounted it becomes awkward and time consuming to adjust the router bit depth from under the table.
One effort to reduce the difficulty of such adjustment contemplates the use of a flexible sleeve enclosing a threaded insert to which different driving socket mechanisms can be engaged, U.S. Pat. No. 5,590,989 to Mulvihill (1997) Flexible Router Height-Adjustment Mechanism. Nevertheless, the adjustment mechanism suffers from a number of disadvantages:                (a) The method is limited to plunge routers.        (b) The threaded sleeve engages the threaded adjustment rod. While this arrangement may decrease the awkwardness and difficulty of adjusting the router bit height relative to the router table, the mechanism does not have a mounting mechanism which can stabilize the adjustment drive method.        (c) Furthermore this method relies on a socket member having a socket opening to provide the driving purpose.        (d) Furthermore the same results can be attained with common mechanic tools, combining a socket with a flexible extension bit holder attached to a socket driver at a much lower cost.        (e) Additionally, the mechanism is structurally complex and expensive to manufacture and still requires additional socket driver attachments to be useful.        (f) The mechanism is limited to only router's having a threaded shaft adjustment mechanism.        (g) The flexible sleeve encloses a threaded insert which can interfere with the engaging threaded shaft adjustment mechanism when the flexible shaft is bent at an abrupt angle.        
Another effort to reduce the difficulty of table mounted plunge router adjustment requires a special table plate attached to the top of the router table and a separate hand crank to perform adjustments, U.S. Pat. No. 6,948,892 B2 to Hummel (2005) Lift Mechanism for Plunge Routers. While this method is effective, it too suffers from a number of disadvantages:
(a) Installation is not always a simple modification to router tables that have solid surfaces, such as those made out of cast iron.
(b) Before the router table can be used, a hand crank has to be removed after each adjustment.
(c) The engagement mechanism which receives the hand crank risks being clogged with saw dust between adjustments.
(d) A hand crank can be easily misplaced within small wood parts when sawdust is expelled by the router.
(e) The mechanism can be dangerous because it requires the woodworker to be relatively close to the cutting bit to perform any adjustments from the top of the router table.
Another effort to reduce the difficulty of table mounted plunge router adjustment requires a major retrofit of a plunge router and is limited to only plunge routers, U.S. Pat. No. 7,052,218 to Christopher John Mussel (2006) Methods and apparatus for adjusting a plunge router. Furthermore the adjustment mechanism requires a cable to raise and lower a router which provides less stability and rigidity when adjusting the height of a router.
Another effort to reduce the difficulty of adjusting a non plunge router, U.S. Pat. No. 7,334,614 to Randy G. Cooper, Mark A. Etter, Greg K. Griffin, Ginger L. Allen, and Derrick Kilbourne of BLACK & DECKER INC. attempts to use a worm drive to adjust the height of the router. While effective, when mounted inverted to a router table, the design depends on an adjustment using a tool above the router table. Furthermore the router is a candidate for a retrofit for the present embodiment thereby enabling the router to be adjusted below the table, attaching to the routers rotating member. Consequently, as with the previous mentioned U.S. Pat. No. 6,948,892 B2 to Hummel (2005) Lift Mechanism for Plunge Routers, the engagement mechanism which receives the tool risks being clogged with saw dust between adjustments. Additionally, a tool required for adjustment can be easily misplaced within small wood parts and sawdust expelled by the router. As previously noted, this mechanism can also be dangerous because it requires the woodworker to be relatively close to the cutting bit to perform any adjustments from the top of the router table.
In conclusion, insofar as I am aware, no router adjustment mechanism for a table mounted router formerly developed provides the advantages of retrofitting a router to a router table as this present embodiment. These advantages include but are not limited to:                (a) Safety, no reaching under router table to make adjustments to power tool;        (b) no special template plate needed for router table;        (c) user can measure height of router bit while adjusting at the same time;        (d) no alteration required to router table top;        (e) works with both plunge and standard fixed base routers;        (f) quick smooth and accurate operation;        (g) no permanent modification to router;        (h) familiar adjustment mechanism for woodworkers, similar to adjusting a woodworkers table saw;        (i) permanent mount, no fumbling for attachment to make an adjustment;        (j) works with less complex and costly standard fixed base routers;        (k) adaptable to rotatable adjustments that move spirally.        